27. The cardiac cycle Flashcards
What should be mentioned in this topic?
Cardiac cycle
Systole
Diastole
- Atrial contraction
- Isovolumetric contraction
- rapid ejection
- reduced ejection
- Isovolumetric relaxation
- Rapid filling
- Reduced filling
Heart sounds
Cardiac cycle
While studying the cardiac cycle, the electrical activity (ECG and action potential), mechanical properties, stages of valve motion, pressure and volume circumstances in the chambers, and sound phenomena will be investigated.
The cardiac cycle is an uninterruptedly repeated process of the heart.
- The cycle is composed of two elements, systole and diastole.
- The systole and diastole of the atria and ventricles do not separate fully in time:
- the systole of the atria appears at the end of the diastole of the ventricles.
- This makes it possible that close to the end of the ventricular diastole a smaller fraction of blood can enter the ventricles.
Systole
Contraction: systole
- During the course of systole the heart displays considerable deformation.
- Under real circumstances the systole is preceded by a twisting movement of the heart musculature followed by a considerable shift of the heart towards the base and back towards the apex.
- Emptying of the ventricles
Diastole
Relaxation: diastole
During diatole the heart fills up again, causes characteristic deformations as well.
An overview of the cardiac cycle (picture)
Atrial contraction (Phase 1)
Cuspidal valves are open; Semilunar valves are closed.
Atrial contraction phase begins after the P-wave (atrial depolarization). Atrial wall is contracted, therefore pressure in the lumen increases. This pumps extra amount of blood into the ventricles through the open cuspidal valves.
70% of the blood passively flows into the ventricles, and the atrial contraction is responsible for only 30% of blood flow
- At this phase, the ventricular muscle is entirely relaxed.
- Aortal blood pressure decreases
Atrial contraction (Phase 1)
(picture)
Isovolumetric contraction (Phase 2)
This phase begins with QRS complex of the ECG trace (ventricular depolarization)
- Ventricular volume is unchanged (isovolumetric phase), but the stretch of the wall is increasing
- The increased wall-tension elevates the pressure in the ventricle, even when atrio-ventricular (cuspidal) valves are closed in this phase.
- Ventricular pressure elevates until it reaches the aortic (and tr. pulmonalis) pressure = end of this phase
Isovolumetric contraction (Phase 2)
(picture)
Rapid ejection (phase 3)
(picture)
Reduced ejection (Phase 4)
Phase 3-4
After the previous phase, semilunar valves open (ventricular pressure is higher than aortic and tr. pulmonalis). Isometric contraction begins:
=ejection
-A major volume of the blood will be put into the aorta and tr. pumonalis. The extra amount of blood will increase the aortic pressure (maximal pressure in the arteries = systolic blood pressure)
Reduced ejection (phase 4)
(picture)
Isovolumetric relaxation (Phase 5)
Due to the relaxation, ventricular pressure drops under the aortic and truncus pulmonalis pressure, at this point semilunar valves will close.
- In the first phase of relaxation, all valves are closed, no blood flow occurs in the heart. This phase is called isovolumetric relaxation (no volume changes)
- Till the end of this phase semilunar valves are closed as well
Isovolumetric relaxation (Phase 5)
(picture)
Rapid filling (Phase 6)
The ventricular pressure is further dropping, and when it gets under the atrial pressure, cuspidal valves will open. At this point rapid ventricular filling begins.
- Semilunar valves are closed, but due to the elastic components of the aorta, the blood (pumped into the aorta in phase 4) is flows further into the arterial system (aortic pressure decreases)
- The major volume of the blood flows into the ventricles in this phase
Rapid filling (Phase 6)
(picture)
Reduced filling (Phase 7)
(picture)
